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Metabolism and Enzymology

On The Regulation of Spinach Nitrate Reductase ¹

Institut für Biochemie der Pflanze, Universität Göttingen, Untere Karspüle 2, Göttingen, Federal Republic of Germany

A coupled assay has been worked out to study spinach (Spinacea oleracea L.) nitrate reductase under low, more physiological concentrations of NADH. In this assay the reduction of nitrate is coupled to the oxidation of malate catalyzed by spinach NAD-malate dehydrogenase. The use of this coupled system allows the assay of nitrate reductase activity at steady-state concentrations of NADH below micromolar. We have used this coupled assay to study the kinetic parameters of spinach nitrate reductase and to reinvestigate the putative regulatory role of adenine nucleotides, inorganic phosphate, amino acids, and calcium and calmodulin.

¹ Supported by the Deutsche Forschungsgemeinschaft. J. S. was the recipient of a fellowship from the A. von Humboldt Foundation.